Project Summary We are developing implantable microphones for assistive hearing devices, which are essential for enabling prosthetic hearing devices such as cochlear implants (CI) and middle-ear implants to become fully implantable. Fully-implanted systems offer significant advantages over conventional devices with external microphones: access to hearing 24/7 (such as when sleeping), which can benefit children's brain development and prevent limitations on activities and lifestyles for all ages; benefit from the external ear's acoustic enhancement to improve hearing in noisy environments; ease of use (less challenges in dexterity); cosmetic appeal. We have successfully developed proof-of-concept prototypes for each microphone design and have demonstrated ease of implantation and high-fidelity responses in fresh human cadaveric ears. In this application we focus on two basic microphone designs, with the goal that at the end of the project they will be ready for large-animal experimentation and/or clinical trials. One is an intracochlear microphone embedded within a cochlear implant that senses inner-ear pressure. The other is a motion-sensing device that attaches to the distal end of the malleus, the umbo, within the middle-ear cavity. The devices are based on polyvinylidene fluoride (PVDF), a piezoelectric polymer. The fabrication of the devices starts with a PVDF film, which is metalized to form electrical contacts to transmit the piezoelectric signal. They are then encapsulated and electrically shielded. The devices, already operating at a useful level, will be modeled, evaluated and refined to perform at a level comparable to hearing aid microphones, with high sensitivity, low noise and flat response over a wide bandwidth.